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equal safety from 4 atmospheres to 2, or from 6 to 3, since the 

 volume of gas tending to be liberated would be the same in each 

 case. Experiment showed that this was the case, and that the 

 danger of rapid decompression depends, not on the absolute 

 difference between the initial and final pressure, but on the 

 proportion between the two pressures. If this proportion is 

 only 2 or 2*3 to 1, the decompression is safe; if, on the other 

 hand, the proportion is 3 or 4 to 1, the decompression is dan- 

 gerous. This is illustrated by the experiments in Table IV. 



TABLE IV 



It will be seen that a rapid drop from 6 to t6 atmospheres 

 produced no symptoms at all, the fall of pressure being 3*4 

 atmospheres, and the relation of the higher to the lower pres- 

 sure being 2*3 to 1. With the same animals decompression from 

 4*4 atmospheres to 1 produced disastrous effects, the fall of 

 pressure being exactly the same as before, but the relation 

 of the higher to the lower pressure being now 4^4 to 1. 



The method hitherto recommended for bringing men safely 

 out of compressed air has been to decompress at a slow and 

 uniform rate. But calculation on the principle already referred 

 to shows that however slow this uniform decompression may be, 

 the difference in partial pressure between the nitrogen dissolved 

 in the tissues and the external air pressure will go on increasing 

 during the decompression. Still more will the proportional 

 difference between the two pressures increase. At the end of 

 the decompression, therefore, the danger, if any, will be at a 

 maximum ; whereas during the first half, or more, of decom- 

 pression time is simply being wasted, or much worse than 

 wasted, if saturation of the body was incomplete, as is nearly 

 always the case in diving. All our experiments confirmed this 

 theoretical deduction. 



